1. Field of the Invention
This invention relates to a method and apparatus for transferring data to and from a magnetic medium, and more particularly to a contact recording slider and a method for operating the contact slider in contact with a magnetic medium with a minimal impact on the magnetic medium and the slider.
2. Description of Related Art
Magnetic recording systems utilizing transducers that are supported by an air bearing layer as the transducers move relative to the surface of a rigid magnetic recording disk are well known in the art. Typically, each transducer is mounted in a slider assembly which has a contoured surface. The air bearing is produced by pressurization of the air as it flows between the disk and the slider, and is a consequence of the slider contour and relative motion of the two surfaces. The purpose of the air bearing slider is to provide a very narrow clearance, preferably with no contact between the slider and the rotating disk. The resulting air bearing prevents or reduces damage that would be caused by the slider coming into contact with the rigid medium during operation. Accordingly, transducers "fly" on a layer of pressurized air at several micro-inches above a rotating disk surface. The closer the transducers fly to the rotating disk surface, the greater the density of magnetic flux changes which can be imposed on the recording medium (i.e., the greater the density of data which can be stored on the rotating disk). While lower flying heights produce greater recording densities, an effective air bearing limits the proximity of the slider to the rigid medium to minimize damage.
Typical sliders of the prior art, as illustrated in FIG. 1, utilize at least two lower rails 1a, 1b having flat surfaces 2 oriented toward the recording medium and extending from the body 5 of the slider. Each of these rails 1a, 1b has a tapered forward surface 3a, 3b oriented against the direction of rotation 4 of the recording medium. The rotating recording medium forces air by viscous effect into the tapered forward surfaces 3a, 3b, and thereby produces a pressure beneath each of the rails 1a, 1b, resulting in the air bearing. Typically, these sliders are gimbal-mounted to a load beam assembly which is attached to an arm at a point defined as the "load point" of the slider. The arm is driven by an actuator which positions the transducer over the recording surface from one data track to another. The arm can move in a linear motion (which is termed linear axis), or it can rotate about a pivot point (which is termed rotary axis). With rotary axis, the slider will be positioned at varying angles with respect to direction of the rotation of the disk as the slider moves over the recording surface in an arc. This angular orientation is referred to as the "skew" angle.
Another example of a magnetic head air bearing slider is provided in U.S. Pat. No. 4,475,135 issued to Warner, et al. (the '135 patent). FIG. 2a is an illustration of a slider in accordance with the '135 patent. The '135 patent discloses a self-loading magnetic head air bearing slider 30 having a tapered leading edge 10. The tapered leading edge 10 in accordance with the '135 patent is provided along the entire leading edge 12 of the slider 30. Two rails 28, 30 have parallel sections 32, 34 up to a "break point", and then have flared sections 36, 38 extending toward the trailing edge 26. The rails 28, 30 are flared to provide a negative pressure region, and thus an improved pressure profile and thereby allow fast lift-off from a disk surface by allowing the load on the slider to be slight at takeoff and to increase as the slider achieves flight speed. The slider of the '135 patent attempts to maintain a substantially constant flying height over all the data tracks on a disk surface. FIGS. 2 and 3 illustrate structures having negative pressure regions.
Other examples of a self-loading slider 40 having a negative pressure region 52 intended to provide an improved the pressure profile are disclosed in U.S. Pat. No. 5,212,608 issued to Yoneoka (the '608 patent) and illustrated in FIG. 2b and U.S. Pat. No. 4,734,803 issued to Nishihira and illustrated in FIG. 2c. A slider 40 as shown in FIG. 2b has two rails 51, 51' which extend from a body 59. The width of each rail 51, 51' is greater near the leading edge, and narrower near the trailing edge. Narrowing the trailing edge of the rails 51, 51' provides the negative pressure region 52 when air enter in the direction shown by arrow 55. Thus, the height at which a recording element 53 flies over a recording medium is stablized. A slider 40' as shown in FIG. 2c has leading edge tapers 66, 66' to aid in generating an air bearing, and rails 60, 60' which produce a negative pressure region 68. These designs provide a flow path in which the area available for air to exit the air bearing is greater than the inlet area. This expansion in flow path area causes an expansion of the air resulting in lower pressure. This lower pressure can be a negative "gage" pressure, or an absolute pressure which is less than the ambient pressure. This negative gage pressure produces a suction force on portions of the slider to provide a downward self-loading force on the slider body. In typical negative pressure structures, air expands into the recess between the air bearing surface rails to create the negative pressure region. The inner edge of each rail forms the recess or negative pressure region.
While lower flying height of a slider produces greater recording densities (i.e., allow more flux changes per inch), an effective air bearing limits the proximity of the slider to the medium. Ultimately, it would be desireable for a slider to be in contact with the medium to acheive the greatest recording density. Such contact is established between a recording head and the magnetic medium of data storage devices which use flexible recording media. For example, U.S. Pat. No. 4,191,980 issued to King et al. (the '980 patent) discloses a transducer with tapered edge profiles for transferring data to and from a flexible magnetic disk. However, it is well known that placing a recording slider in contact with a rigid recording medium damages both the recording medium and the slider and thus reduces the life of the data storage device.
Furthermore, conventional sliders suffer from the following disadvantages: (1) Asperity contact, (2) Stiction, and (3) Transverse flow.
Asperity contact--Although air bearing sliders fly on an air bearing as described above, they nonetheless contact the medium during take-off and also contact asperities or contamination during steady flight. These asperities (i.e., protrusions and protuberances which rise above the magnetic disk surface) are higher than the flying height of the slider and contact the air bearing slider rails causing damage to either the recording medium or the slider rail. Furthermore, such sliders typically have a load point (i.e., the point at which a downward force is applied to the slider to prevent the slider from flying at too great a height over the magnetic disk surface) which is generally located on the air bearing slider at a point which is closer to the trailing edge than the leading edge of the slider. The slider typically gimbals about the load point. Damage may occur if the slider pitches down and "plows" into the disk surface. That is, if the leading edge of the slider makes contact with the disk surface due to a forward pitching motion during flight. Even in instances when the slider does not pitch down, but rather contacts an asperity at the desired attitude, the contact may be damaging to the slider and medium. In the best circumstance, a slider makes contact with an asperity on the air bearing surface while pitched upward with the leading edge above the trailing edge. In such a case, the force that is generated by the impact may still exceed the yield limit of the material and cause plastic deformations or fracturing of the material. Once this type of damage begins, repeated contact of such a slider with asperities on the medium accelerates the break-up of the thin, hard coating on the disk surface and head crashes may ensue.
Stiction--Conventional sliders have a reliately high stiction between sliders and a magnetic medium. Plots of stiction over thousands of "contact stop start" (CSS) cycles show a pronounced increase in the stiction value of conventional designs with age. FIG. 3 shows such CSS data for a slider representative of the current art. The increase in stiction corresponds to a degradation of the medium surface. Damage is caused as the slider shears or fractures asperities before flight is achieved. Higher stiction values result in higher lift-off torque values, which, because the load point is above the medium surface, causes the slider to "nose down" before take-off. This nose down force produces a greater "plowing" of the media by the nose of the slider.
One mechanism which contributes to stiction is the amount of energy required to deform or shear asperities that constitute the real area of contact between the slider and the medium when the slider is not in flight. It is believed that this is due to shearing forces generated between the sides of the slider and the inner wall of a depression in the recording medium that is created when the slider is impressed slightly into the material of the recording medium. In order to pull the slider from the recess that is created by the force of the slider which is at rest against the recording medium, the slider must overcome the shearing forces that are generated by the edges of the slider grating against the edges of the recess. Still further, sharp edges of the air bearing surface produce stress concentrations in the medium. These stress concentrations increase the depth of sheared regions, causing severe damage. Also, these sharp edges act as a knife edge seal which prevents air from entering underneath the slider as disk motion is initiated. This sealing further inhibits the take-off of the slider and increases the contact between the medium and the air bearing surfaces as the medium starts to move with respect to the slider. This increased contact, together with other forces between the slider and the recording medium, causes damage to the medium and to the air bearing surfaces of the slider.
Transverse Flow--Transverse flow occurs when a conventional slider is oriented at non-zero skew angles or when a slider is moved radially across the medium. When conventional sliders are flown at a skew angle other than 0.degree., or when a conventional slider moves radially at a relatively high velocity, transverse flow occurs under the air bearing surfaces. Such transverse flow causes conventional sliders to roll and makes it difficult to maintain a constant flying height. In order to correct for the effects of such transverse flow, so-called "constant flying height" designs have been proposed. Although these have not demonstrated truly constant flying height over the operational range of skew angles, they do desensitive the slider's flying height to the skew angle. One such "constant flying height" design incorporates transverse pressure contour (TPCs). For example, in U.S. Pat. No. 4,673,996 ("the '996 patent"), a range of contours are disclosed. While these contours provide some improvement in the flight of a slider, fabricating the fairly precise angles or angular structures required to form the transverse pressurization contour on an air bearing edge is problematic.
Therefore, it would be desirable to provide a slider which is less susceptible to damage from transverse contact with asperities, which has fast lift-off from a disk surface, is less susceptible to transverse air flow, provides high recording density, reduces stiction of the slider to the disk surface, and is inexpensive and simple to fabricate. The present invention provides such a slider.